Hutchinson, Bevis

Abstract [en]

The aim of this study was to develop and investigate low carbon bainitic hot strip steels microalloyed with vanadium and suitable base alloying. The processing conditions chosen in the laboratory investigation correspond to typical 8 mm hot strip processed in a conventional hot strip mill or in a compact strip processing mill with hot charging. It was found that a base alloying of 1.4%Mn, 1.0-1.4%Cr and 0.12-0.25% Mo is required to form a fully bainitic structure during cooling after finish rolling. For steels coiled at 400°C the bainite formation is complete before coiling while for higher coiling temperatures, more bainite will gradually form during the coiling. For steel with this base alloying together with 0.08% V and 0.010-0.020% N the yield strength lies in the range of 750-790 MPa for a coiling temperature of 400°C, whereas it is 680 MPa for a similar steel without vanadium (reference). For the lower nitrogen content, 0.010%, the difference in strength level between the vanadium steel and the reference is only marginally reduced at higher coiling temperatures, whereas for the higher nitrogen content this difference decreases with increasing coiling temperature. By raising the chromium content to 2%, yield strengths in the range of 840-880 MPa have been reached. This is attributed to a lowering of the bainite transformation temperature resulting from the higher base alloying.